A Bε-tree is an example of a write-optimized data structure and can be used to organize on-disk storage in general, and can be suitable in applications such as databases and file systems. The database or file system can comprise a key-value store that allows users to store and retrieve data in the form of key-value pairs. The “key” in a key-value pair can be an index (e.g., number, string, etc.) that uniquely identifies its paired “value.” The value in a key-value pair can be any type of data object or collection of data objects. A Bε-tree can provide a key-value application programming interface (API) to provide insert, range query, and key-value update operations on the key-value store.